1. Field of the Invention
The present invention relates to a prismatic cell and an assembled battery using the prismatic cell.
2. Background Art
In recent years, a cell-powered car using a secondary cell as a power source, such as an electric vehicle (EV) and a hybrid electric vehicle (HEV), has been becoming popular. However, a high power secondary cell is required for such a cell-powered vehicle.
For usage requiring high output such as EV and HEV, a battery pack (assembled battery) has been used in which multiple cells are connected in series and/or in parallel. In connection of multiple cells, a prismatic cell is more excellent in space efficiency than a cylindrical cell. Therefore, a prismatic cell is often used as a cell constituting an assembled battery.
In addition, because a high-output cell requires stable extraction of current and easy connection of a plurality of cells, there is used a configuration in which its positive and negative electrode external terminals are protruded and insulated from a sealing body.
In the case that a plurality of the cells are connected to form an assembled battery, when an outer can of the assembled battery is polarized due to a contact with an electrode assembly housed therein and so on, a short-circuit may occur by a contact between the outer can and another can that is charged with opposite polarity. To prevent this short circuit, Patent Documents 1 to 6 have proposed technologies in which side and bottom surfaces of the outer can are insulatively covered.    [Patent Document 1] Japan Patent Application Publication No. 2002-184364    [Patent Document 2] Japan Patent Application Publication No. 2003-223872    [Patent Document 3] Japan Patent Application Publication No. 2004-319260    [Patent Document 4] Japan Patent Application Publication No. 2006-120419    [Patent Document 5] Japan Patent Application Publication No. 2006-269425    [Patent Document 6] Japan Patent Application Publication No. 2008-166191
Patent Document 1 discloses a technology in which a resin film overlaps only on one of the side surfaces of a bare cell along the bare cell, and the overlapped part is bonded by at least one of a heat seal, a glue or an adhesive, and then the side surface of the bare cell and the resin film are attached to each other or heated after covering, and thereby the resin film is formed so as to have shrinking stress. It is described that this technology allows attachment of an exterior film without a decrease in space efficiency.
Patent Document 2 is characterized as follows. A shrink film drawn in a tube-like shape is cut to a predetermined length, and the lithium ion secondary cell body is put into this shrink film, and further the shrink film is sealed in a sack-like shape at the edge of the negative electrode side of the cell, or is formed in a belt-like shape, in order to cover the periphery of the lithium ion secondary battery body including an insulative lid member with the shrink film by means of heat shrinking. It is described that this technology allows a rapid and stable covering.
Patent Document 3 is characterized as follows. At least one surface of long side surfaces, short side surfaces, a bottom surface, and a lid surface, constituting a secondary cell container for housing a cell element such as an electrode, an electrolyte or a separator, are formed of different materials of metal-resin composite plate or thermoplastic resin. And a contact part of a metal-resin composite plate wall surface with a thermoplastic resin surface is integrally formed of the metal-resin composite plate and the thermoplastic resin. This technique provides a secondary cell container that overcomes the drawbacks of lowering adhesion strength during hot-cold cycle, and that excels in a water vapor barrier property and a gas barrier property against gases such as hydrogen and oxygen generated in the cell, and that excels in radiation of heat generated during charging and discharging of the cell.
Patent Document 4 discloses a technology in which a barrier member for preventing moisture permeation is provided at least at a corner of a case whose external surface is covered with an outer package film. It is described that this technology allows to prevent moisture permeation from the corner portion of the case.
Patent Document 5 discloses a technology in which a group of electrodes is housed in a case where an insulation layer including an oxide coating is formed on its surface. It is described that this technology can provide a secondary cell with improved structural safety and reliability as well as insulation property.
Patent Document 6 is characterized as follows. A periphery of an outer can is covered with a plurality of separators that have electric insulating characteristics and heat insulating characteristics. Each separator is interposed between mutual cells so that the outer can is contacted with both faces of the separators. And the electrode terminal is exposed with the outer can covered with the separators, and thereby this part is connected. It is described that this technique allows to cover the periphery of the cell except an area that is not necessary to be covered, and to effectively prevent an unintended short circuit and the like.